Blind fasteners are utilized in fastening workpieces in which only one side of the workpiece is accessible. One such fastener, described in U.S. Pat. No. 5,131,107, issued to Pratt, et al, includes a stem and fastener body or sleeve which are inserted as a unit into aligned openings in workpieces. The stem is an elongated body having one end or tail designed for gripping by a pulling tool. The opposite end of the stem has an enlarged head. A shear ring is mounted on the end of the stem near the head, and a lock ring is located near the middle of the stem.
The sleeve has a preformed head which engages the accessible side of the workpieces, and a tail which is designed for engagement of the blind side of the workpieces. The stem is inserted in the tubular body with the shear ring engaging the body tail and the stem tail protruding beyond the fastener body head.
To install this blind fastener, the stem and fastener body are inserted into the workpiece opening until the head of the fastener body engages the workpiece. The pulling tool is used to grasp the stem tail, and a force is applied to pull the stem through the sleeve with the tool nose reacting against the fastener body head. As the stem is pulled, a bulbing portion of the shear ring slides within the tail of the fastener body, causing the tail to bulb radially outwardly. The shear ring is constructed such that after the bulbing is completed and a predetermined compressive force is applied to the workpieces through the shear ring and the bulbed tail, the shear ring separates from an anchor portion of the ring.
Continued pulling causes the stem to slide through the sheared ring and move further within the fastener body. This enables the fastener to be used with workpieces having a variety of thicknesses. As the stem moves within the fastener body, a neck on the stem encounters a slightly reduced diameter portion of the fastener body interior, causing radial expansion of the fastener body, aiding in the filling of any gap or clearance between the fastener body and the workpieces.
As the stem reaches its installed position, the lock ring encounters an anvil on the pulling tool, causing the lock ring to be compressed into a small recess at the end of the bore in the fastener body. When the lock ring has fully deformed, continued pulling increases the load causing the tail of the stem to break away at a break groove located beyond the lock ring at that point.
The fastening procedure is then complete. The radial pressure from the stem against the reduced diameter portion of the fastener body creates a tight fit between the stem and the fastener body, and has improved the fit between the fastener and the workpieces. The workpieces are held securely together by the tension in the fastener body created by the heads on the body. The stem is captured within the fastener body by the shear ring and the stem head at one end, and the deformed lock ring at the other.
While the fastener described in U.S. Pat. No. 5,131,107 has some workpiece hole filling capability because the interference between the stem and the sleeve radially expands the sleeve, greater hole filling capability is desirable, because of variations in workpiece hole size. Also, tolerance must be maintained fairly closely in that too much interference between the stem and sleeve could cause premature "locking" of the stem in the sleeve and cause the stem to sever before it has reached its fully installed position. While the manufacturer of the fastener can maintain close tolerances in the stem diameter and inner and outer sleeve diameter, the manufacturer cannot oversee the creation of the hole into which the fastener is to be installed.
U.S. Pat. No. 4,627,775 issued to Dixon discloses a fastener which provides hole fill capability with formation of a lock ring. That patent describes a blind fastener having a pin and sleeve arrangement, but does not employ a preformed lock ring. Instead, major interference is created between the pin and the sleeve causing expansion of the sleeve to fill the gap between the sleeve and the workpieces. This interference also results in sleeve material being sheared away and moved into a lock groove to form a lock between the pin and sleeve.
An annular extruding land, or enlarged section, is formed on the pin adjacent the lock groove and on the side of the stem towards the fastener head. When the stem is pulled through the sleeve, the extruding land interferes with the inner wall of the sleeve. This causes the sleeve to expand outwardly and fill any space between the outside of the sleeve and the workpieces. At the same time, the land shears material from the wall of the sleeve. This material is pushed ahead of the land into the lock groove. When the pin is fully installed, a stop land encounters the surface of an installation tool anvil, and further pulling causes the serrated end of the pin to separate at a break notch. At this time, the material sheared from the sleeve sufficiently fills the lock groove so as to prevent removal of the pin from the sleeve.
One drawback of the device described in the Dixon patent is that the shearing action necessary to create the locking ring is made difficult when the sleeve is made of a very tough metal or alloy. If the sleeve is made of a particularly durable alloy or metal, the pulling force necessary to shear the sleeve material may be so high that the pin severs at the break groove before installation. Related to that, considerable interference is needed to provide enough material for workpiece hole fill and to provide the stem locking function.
Thus a need exists for a fastener that overcomes the above-described limitations and problems of prior art fasteners.